There exists a great need for copper alloys for use for electrical purposes. These alloys are, among other things, needed as base materials for semiconductors, for example for transistors or integrated circuits. Base materials for semiconductors should have a particular combination of characterisics:
A. The mechanical strength must be sufficiently high so that a shape stability of the base is assured during the manufacture and also during the equipping with electronic elements. The need for strength increases mainly when the number of small connecting legs is high, because their regular alignment is of crucial importance for the automatic manufacture and equipping with elements.
B. The material must resist softening, so that the manufacturing steps needed during the semiconductor production, which steps are carried out at a higher temperature, do not lead to a loss of hardness and shape stability.
A measure for the softening resistance is the so-called half-hardness temperature T.sub.H which, according to FIG. 1, is obtained from the softening curve (Vickers hardness HV as a function of the annealing temperature T). The half-hardness temperature T.sub.H is thereby associated with the value ##EQU1##
A thermal stress occurs substantially during the fastening of the semiconductor part on the base, when the adhesive is hardened or a euctectic reaction is caused between the silicon element and a gold coating of the base. Furthermore, higher temperatures occur during the connection of the semiconductor part with the small connecting legs using so-called bond wires, and during pressing of the complete building element into plastic. Temperatures of up to 400.degree. C. can occur for long periods of time during these manufacturing steps. Therefore, no noticeable softening may be found in semiconductor materials below 350.degree. to 400.degree. C. As a rule, a hardness reduction of at most 10% of the initial hardness is permitted.
C. The electrical and thermal conductivity should be as high as possible, so that the power loss which is created on the silicon semiconductor during operation can be discharged in the form of heat and thus a self-destruction of the semiconductor is prevented. In order to assure the necessary degree of heat conduction, the electrical conductivity should lie, as much as possible, above 40% IACS (where 100% IACS corresponds to 58.00 m/Ohm.mm.sup.2).
D. Homogenous materials are increasingly required, mainly for nonpurified semiconductor bases. This means materials having structures which do not contain any separations or inclusions, so that a satisfactory bond wire connection is assured. This avoids the uncertainty that the bond wire may hit such nonhomogeneities, which would cause the adhesion to worsen and the contact resistance to change. In order to increase the manufacturing and functional quality, homogeneous materials are being increasingly demanded for the field of application of semiconductor bases.
To date in the mentioned application, copper-iron-alloys, for example CDA 194, CDA 195 and other low-alloyed Cu-materials, for example CuNilSnlCrTi, have been utilized extensively. These materials have a sufficient hardness and good electrical conductivity. However, the structures of these materials contain clearly visible, and as a rule rectilinear, separations which can interfere during bonding. Bond wires which are completely or partially applied to these nonhomogeneties cannot meet the required electrical functionality or the required reliability, since the contact resistance is changed and the adhesive strength is worsened. Low-alloyed materials such as CuZn0.15, CuSn0.12 and CuFe0.1 are homogeneous and do not have the above-mentioned disadvantageous structural nonhomogeneities, but do have a strength which is too low for many fields of application.